The objective is to improve the effectiveness of measles and tetanus vaccines in developing countries, thereby diminishing mortality and debility there, reducing measles virus importation to the USA and learning more about the identity of the immunoglobulin which protect against measles and the factors which control their transport to the fetus. Specifically we will: 1. Identify the factors(s) which determine the age at which a child becomes susceptible to measles and responsive to vaccine. 2. Study the relative roles in protection from disease of immunologlobulin idiotypes directed toward the four major structural proteins of measles virus. 3. Quantitate the response of the human adult to repeated doses of tetanus toxiod and to set up practical guidelines for determination of vaccine needs in diverse populations. 4. Seek to learn more about the mechanism of transplacental movement of immunoglobulins in humans.